Will the State of the Union be postponed? That hasn’t happened since the Challenger disaster.

As a federal shutdown lumbered through its fourth week, House Speaker Nancy Pelosi (D-Calif.) on Wednesday sent a letter to President Trump urging him to postpone his Jan. 29 State of the Union address because of shutdown-related security reasons. Perhaps Trump could deliver his speech in writing that day, Pelosi suggested.

The letter was immediately described as a “power move” against Trump and as Pelosi “playing hardball” by threatening to deprive the president of both a stage and an audience. Meanwhile, the GOP decried it as “unprecedented” partisanship, with some (including Trump’s eldest son) accusing Pelosi of attempted censorship.

Pelosi waved off criticisms, maintaining she was genuinely concerned about security and gently twisting the knife further by telling reportersTrump could “make the speech from the Oval Office instead, if he wants.” As of Wednesday afternoon, the White House still had not responded to the letter.

But postponing a State of the Union speech is not unprecedented. It last happened more than three decades ago — though at the time it was rescheduled because of an unthinkable national tragedy.